The invention relates to a method of tuning a microcomputer-controlled radio receiver to the one of several transmitters broadcasting the same program best satisfying reception quality requirements by making use of RDS information and preferably by using only one receiving section. The method according to the invention is particularly intended for application in mobile radio receivers, especially car radios.
Since the availability of RDS information it has become possible to automatically tune also radio receivers having merely one receiving section to the one of several transmitters broadcasting the same program best satisfying the requirements of reception quality. The RDS information also facilitates achieving radio receivers having two receiving sections, one of which is continuously involved in checking the alternative transmitter frequencies transmitted in the RDS information.
To be able to select from the alternative transmitter frequencies as contained in the RDS data stream the one actually having the best quality of reception, each of the individual alternative transmitter frequencies must be tested. Since up to 40 alternative transmitter frequencies can be identified to the transmitter set in each case, checking all of the frequencies necessitates a time duration of considerable length. Although the quality of reception of a transmitter can be measured relatively quickly on the basis of the field strength and other signals indicating the occurrence of noise in reception (multi-path reception, adjacent and co-channel noise), determining the identity code of a transmitter set for checking takes up a time period of up to 1 second. Checking the identity code is necessary, however, since due to random overlapping of reception sectors ambiguities may arise. Due to special conditions of reception it is possible that a program can be received under a given frequency contained in the RDS data stream which is different to that to which the transmitter is momentarily tuned, the alternative frequencies of which are included in the data stream.
Since checking the quality of reception and the identity code of all alternative frequencies listed in the RDS data stream necessitates a considerable time period there is the problem particularly in mobile radio receivers that the information obtained in checking the alternative transmitters is no longer current at the moment at which tuning to an alternative transmitter is required, due to the quality of reception of the transmitter tuned momentarily deteriorating. This problem is particularly serious in radio receivers having only a single receiver section since this is to be tuned to an alternative frequency only for a very brief time so that the changeover does not become a nuisance. Checking the identity code is only possible when the receiver remains tuned to the alternative frequency for a time period of at least a few hundred milliseconds which requires that the quality of reception is sufficient.